A site in the western flank of Jabal Ja'alan (Oman Mountains) reveals an exceptional succession across the Cretaceous-Paleogene boundary. The sampled interval comprises a series of carbonates deposited in shallow-water platform environments and belonging to the Murka Formation, which lies between the Simsima and Abat formations of latest Cretaceous and Thanetian age, respectively. The larger foraminifera recovered from this interval belong essentially to the group of larger rotaliids (Rotaliidae). Two new genera and two new species are here described, Praelockhartia neoakbari gen. nov., sp. nov. and Rotaliidium parvum gen. nov., sp. nov. The former shows a very characteristic architecture of an umbilicus with strong piles and two types of umbilical cavities, while the latter has characteristic dorsal supplementary chamberlets. Other species such as Rotalia cf. jacobi, Rotorbinella hensoni, Rotospirella conica and Lockhartia sp. complete the rotaliid assemblage. The entire assemblage can be considered to be of late Danian age and to belong to shallow benthic zone SBZ 2. The larger rotaliids appear to have recovered and diversified earlier than any other larger benthic foraminifera in the region after the K/Pg crisis. The rotaliids from the Murka Formation also appear to be linked to the Lockhartiinae and to play a special role in improving our understanding of subsequent diversification in the Lockhartia Sea. A new subfamily, Praelockhartiinae, is erected to accommodate all primitive forms that are architecturally close to lockhartiids.
This study examines the distribution of larger foraminifera in an upper Campanian-lower Maastrichtian siliciclastic-carbonate depositional environment within the Arén Sandstone Formation. Three assemblages have been identified, which refer to prodelta, reef, and lagoon depositional facies. Prodelta deposits are characterized by Lepidorbitoides socialis, Lepidorbitoides aff. minor, Clypeorbis mammillata, and Siderolites cataluniensis. The reef deposit assemblage contains Siderolites calcitrapoides, Siderolites cataluniensis, Orbitoides gruenbachensis, ''Orbitoides'' aff. concavatus, Lepidorbitoides aff. minor, and Fallotia jacquoti. They are associated with the encrusting foraminifera Solenomeris and Haddonia. The lagoonal assemblage contains Fascispira colomi and Omphalocyclus macroporus. Among the siderolitids, the keeled saucershaped Siderolites cataluniensis colonized the deepest environments at the lower photic zone, whereas the canaliculate spine-bearing Siderolites calcitrapoides characterized shallower waters. The former lived on soft media of calm environments whereas the latter crawled on firmground of high-energy environments. Lepidorbitoides socialis shared with Siderolites cataluniensis and Clypeorbis mammillata the deepest, calm environments, while Lepidoritoides aff. minor adapted to a wide range of depths in low to moderate water-energy environments. Orbitoides gruenbachensis and ''Orbitoides'' aff. concavatus colonized the firm media in the upper photic zone, whereas Omphalocyclus macroporus was an epiphyte in soft media in areas with a moderate-energy water. The meandropsinids occupied the upper photic zone; the odd pair Fallotia jacquoti and Eofallotia simplex colonized high-energy environments, whereas their relative Fascispira colomi adapted to shallow, calm environments. The structure of the assemblages of larger foraminifera described in this paper provides a useful tool for the reconstruction of the Late Cretaceous shallow-water fauna in mixed siliciclastic-carbonate environments.
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